The present invention relates to a composite anode used for nonaqueous secondary batteries and particularly to a composite anode used for nonaqueous secondary batteries which is formed using a pulverized alkali metal alloy, a carbonaceous material powder and a polymeric binder and a method for producing the same.
The improvement of charge-discharge cycle life is the most important task to be attained in the nonaqueous secondary batteries in which an alkali metal is used as an anode active material and a solution prepared by dissolving an electrolyte in an organic solvent is used as an electrolyte solution. In order to inhibit the side reaction between the electrolyte solution and the active alkali metal precipitated on the anode upon charging which is a factor governing the charge-discharge cycle life, it is necessary to select the optimum combination of the anode and the electrolyte system. Accordingly, as for the electrolyte system, development of a mixed solvent system and an electrolyte solution excellent in the stability on the anode or research on the additives for inhibiting the side reactions has been attempted. As for the anode materials, in order to prevent the active alkali metals from precipitating on the surface of the anode at the time of charging, it has been studied to use alloys of alkali metals or carbon materials as the anode materials to rapidly diffuse into the alloy or carbon the alkali metal precipitated by the charging, thereby to inhibit the reaction between the electrolyte solution and the alkali metal.
However, when novel anode materials are developed, the problem in use of the carbon materials is that they are low in capacity density per volume of the electrode. In the case of using alkali metal alloys, when the anode utilization is enhanced, the alkali metal alloys undergo change in volume due to the charge-discharge and repetition of the charge-discharge results in collapse of the electrodes to cause decrease in the charge-discharge cycle life.
In order to solve these problems, hitherto there have been proposed a method of using a composite of an alkali metal alloy and a conductive polymer (Japanese Patent Kokai (Laid-Open) No. 60-262351) and a method of forming the electrode using a PTFE resin as a binder (Japanese Patent Kokai (Laid-Open) No. 60131776).
However, these methods suffer from the problems that, for example, conductive polymers release alkali metals at the time of discharging to cause decrease of conductivity and sufficient interparticle bonding effect cannot be obtained because of their small specific surface area of about 10 m.sup.2 /g and when a PTFE resin is used as a binder, this resin reacts with the alkali metal to bring about deterioration of the anode.